1. Field of the Invention
The present invention relates generally to a liquid droplet ejecting method using a liquid droplet ejection apparatus which ejects liquid in the form of minute droplets from an ejection opening through pressurization of the liquid within a pressurizing chamber, and to a such liquid droplet ejection apparatus. More particularly, the present invention relates to a liquid droplet ejecting method and a liquid droplet ejection apparatus for ejecting the minute liquid droplets over a plurality of times through repetitive intermittent operations of pressurization.
2. Description of the Related Art
The liquid droplet ejecting method of this type is disclosed in, for example, Japanese Patent Application Laid-Open (kokai) No. 2001-186880. The technique disclosed in this gazette includes filling a pressurizing chamber with liquid (DNA fragment solution) containing DNA fragments, and driving a piezoelectric/electrostrictive element disposed on the wall surface of the pressurizing chamber, thereby changing the volume of the pressurizing chamber so as to pressurize the liquid within the pressurizing chamber, to consequently eject the liquid as minute liquid droplets from the ejection opening in liquid communication with the pressurizing chamber so that liquid droplets are formed on a substrate such as a microscope slide glass confronting the ejection opening. This liquid droplet ejecting method comprises setting to a minute amount the amount of liquid droplet ejected (i.e. ejecting a predetermined minute amount of liquid droplet) by a single operation of pressurization (ejecting operation) and intermittently repeating the operation of pressurization so that the minute liquid droplet drops onto the substrate at the same spot over a plurality of times. The number of operations of pressurization is adjusted so as to allow the amount of a single liquid droplet and/or the diameter of the liquid droplet formed on the substrate to precisely be controlled.
In the above disclosed liquid droplet ejecting method, the pressurizing rate (or speed) in each operation of pressurization (applied voltage changing speed when the pressurizing means are the piezoelectric/electrostrictive element) is constant, and thus the ejecting speed of the minute liquid droplets ejected is unvaried. For this reason, in case of ejecting liquid whose viscosity varies with the lapse of time, such as the liquid containing DNA fragments, the ejecting force becomes excessively large when liquid with lower viscosity is ejected, if the pressurizing speed is set to a level appropriate for higher viscosity, with the result that more minute liquid droplets scatter at the ejection opening end in directions different from the main direction of ejection, which may possibly reach other adjacent liquid droplets on the substrate. On the contrary, if the pressurizing speed is set to a level suited for lower liquid viscosity in order to obviate the above scattering, the ejecting force becomes excessively small when liquid with higher viscosity is ejected. As a result, whereupon the direction of ejection of the liquid droplets may possibly differ from the target direction.